Exchange - Update legacy mailbox on child domain

So I had a sudden need to migrate a mailbox from a legacy Exchange 2003 server to a 2007 server within the same Exchange organization but this particular mailbox resided on a sub/child domain.

First I needed to see this legacy mailbox via the EMC.  Click on Recipient Configuration




Then via the actions pane, select Modify Recipient Scope to and extend the EMC view to the entire forest.



Then finally after the mailbox has been successfully moved, I was able to update the legacy mailbox and specify the dc of our child domain.  If the dc is not specified, the process will error out.

set-mailbox -id mailboxusername -applymandatoryproperties -domaincontroller dcname