PowerShell Scripting Arrays with ForEach

I am trying writing a PowerShell script to disable inactive user accounts using arrays.

I found this bit of code on TechNet which parses each domain controller:
# Get the list of all the domain controllers for the current domain
$DCs = [System.DirectoryServices.ActiveDirectory.Domain]::GetCurrentDomain().DomainControllers
foreach ($DC in $DCs)
{
# Set in the LDAP URL the DC hostname and the container DN specified on the command line
$LdapURL = "LDAP://" + $DC.Name + "/" + $Subtree
# Initialize a DirectorySearcher object
$searcher = New-Object System.DirectoryServices.DirectorySearcher([ADSI]$LdapURL)
.
.
}

This code works but requires that I enter the $Subtree (DN of the OU containing the User objects).  
What I need to do is parse the parent OU of the OU containing the user objects and parse through that one too.
Example (Active Directory view -/+ = expand/collapse):

-mydomain@domain.com
     -COMPANY (OU)
         -Region 1($regOU)
             -FAC_ID1 ($siteOU)
                 Users (user objects)
             -FAC_ID2 ($siteOU)
                 Users (user objects)
             +FAC_ID3 ($siteOU)
         -Region 2($regOU)
               -FAC_ID1 ($siteOU)
                  Users (user objects)
              +FAC_ID2 ($siteOU)
              +FAC_ID3 ($siteOU)
         +Region 3 ($regOU)
         +Region 4 ($regOU)
.
.
.
I am thinking the new code should look something like this:
foreach ($DC in $DCs)
{
  foreach ($regOU in $regOUs)
  {
   foreach ($siteOU in $siteOUs)
    {

How do I identify/assign the $regOUs and $siteOUs array values in PowerShell?  
The $siteOUs array could contain upwards of 10 OU objects per ever 1 $regOU (and there are multiples of those too).

Let me know if you require any addition details or clarification.  Thanks