DNS change affecting all but 1 computer on network

I recently moved a differently themed version of my website to a new host. This morning I pointed the DNS to the new host.

I have four computers on one network: two Macs, one PC, and an iPhone. When pointing any browser to my domain name for the last four hours, three of my computers are showing me the new site on the new host, but one of my computers -- a Mac -- keeps showing me the old site on the old host. I've emptied browser cache and I've restarted the Mac, but I still can't see the new site on any of its browsers.

When I restart the Mac from a different startup disk, I do see the new site on the new host. When I switch back to my regular drive, I again see only the old site on the old host.

When I switch my iPhone to AT&T's data network, it shows me the new site at the new host.

I've even tried pinging my domain name from the computer that stills shows the old site. The IP address that the pings come back from is that of the old host. When I do the same on one of the other computers, the pings come back from the new host.

This makes no sense to me. Can anybody make any sense of what's happening here? Thanks.
Jonathan GreenbergAsked:
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CompProbSolvConnect With a Mentor Commented:
Have you checked what the Mac is using for DNS?  If it is pointing to a different site than the PCs, this would explain it.  When that DNS eventually updates, it should change to the correct site.

I don't know Macs at all, so can't give you the commands to check this.
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strungCommented:
You may need to clear the DNS cache on the Mac.

Assuming the Mac is running OS 10.5 or newer, open Terminal.app (found in /Applications/Utilities) and copy and paste the following line into the window, then hit return:

dscacheutil -flushcache
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Jonathan GreenbergAuthor Commented:
Thank you, strung. I've already done this. I then relaunched browser, but there's no change. I haven't restarted since doing this, I suppose that may be worth a try.

Thanks.
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strungConnect With a Mentor Commented:
To check the DNS Settings on the Mac, pull down the Apple Menu to System Preferences and click on Network Preferences.
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strungCommented:
Then click on the Advanced button and the DNS tab.
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Jonathan GreenbergAuthor Commented:
Yes, I think it may be the DNS settings. The Mac giving me the problem has two DNS servers and one Search domain, but they're all greyed out. And they're all different fro the DNS settings on my Mac that's working. strung, have you any idea how to clear these?
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strungCommented:
If they are greyed, they are probably being obtained by DHCP. Check the TCP settings. Are you perhaps on the wrong subnet or pointed at the wrong router?

Alternatively, you can force the Mac to use a particular DNS server by clicking the + button on the bottom right of the DNS page and manually add the DNS IP address you want.
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Jonathan GreenbergAuthor Commented:
Found it!

I use Dynamic DNS to maintain a domain name with a non-static IP address, and I use their Mac client, called DynDNS Updater. One of the DynDNS Updater preferences is Internet Guide: Set my DNS servers. Unchecking that set the DNS system preferences back to my network's default settings.

Now I'm seeing the same version of my site on this computer that I see on my other computers.

I'm no dummy, but this one had me stumpted. CompProbSolv and strung: thank you both very much!
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