Autodiscover still pointing to internal Exchange after Office 365 migration

Hi,

We have just performed a cutover migration from an on premise Exchange 2010 server to Office 365.  The mailboxes came across ok so we then imported the domain into Office 365 and chose the options to point the domains name servers to 365 so the DNS records would be set up correctly. This change occurred 4 hours ago.  We can successfully connect Outlook 2016 to the 365 mailboxes outside of the network but inside the network Outlook keeps looking at the old autodiscover record (autodiscover.mydomain.com) which of course is wrong.

I have created a CNAME record in the internal DNS of the domain controller and pointed autodiscover.domain.local to autodiscover.outlook.com

I have also run the following command in EMS: Set-ClientAccessServer –Identity “ourexchangeservername” –AutoDiscoverServiceInternalUri $NULL

If I perform an nslookup inside the network on autodiscover.domain.com it comes back with:

Server:  server001.domain.local
Address:  192.168.1.2

Non-authoritative answer:
Name:    autodiscover.domain.com
Address:  External IP of Exchange Server

If I perform an nslookup of autodiscover.domain.local the result comes back as:

Server:  server001.domain.local
Address:  192.168.1.2

Name:    autodiscover-emeawest2.outlook.com
Addresses:  2a01:111:f400:50fa::8
          2603:1026:200:29::8
          2603:1026:0:1::8
          2a01:111:f400:9400::8
          2603:1026:4:14::8
          2603:1026:4::8
          2a01:111:f400:9866::8
          2a01:111:f400:9846::8
          2a01:111:f400:9448::8
          2a01:111:f400:521f::8
          132.245.213.56
          132.245.57.24
          132.245.31.248
          40.101.17.120
          40.101.36.24
          157.56.255.232
          40.101.40.216
          40.101.40.40
          132.245.226.248
          132.245.225.104
Aliases:  autodiscover.domain.local
          autodiscover.outlook.com
          autodiscover.geo.outlook.com
          autodiscover.outlook.com.g.outlook.com

I have flushed and re-registered DNS on the server, restarted DNS server service and restarted the server itself.  I have also as an experiment added the registry entry HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover]
"ExcludeScpLookup"=dword:00000001 on a test PC but that didn't work.

Would really appreciate some help with this if you can...is it just an external DNS propagation delay perhaps?

Thanks

Adam