Also do a metadata cleanup to remove all the retiredDCs (in fact, do that before deleting the sites)
EDIT – check for any site level GPOs too
Meant to come back way earlier than today and say that I did this. Very many thanks to you, sir… Luckily, I checked for site level GPO’s and we didn’t have any.
That, in fact, is my current project. Due to the “centralization” of my company, we’re not using, I’d say, but half of the former GPO’s that are in place. It’s time to go clean them up!