About 9 months ago I became sys admin over Active Directory for a company. Today someone submitted a ticket pointing out that our DNS had a stale entry for an authoritative server. My investigation found that in 2012 a branch office had been closed and the domain controller in that office had been decommissioned without running dcpromo and removing the DNS role. I also found about a dozen and a half other static DNS entries from the same subnet that office ran on, which subnet is no longer used by the company.
This isn't the first time I've encountered static DNS entries that are years out of date. Most of these belong to our engineering unit, who will stand up a server in their lab, request us to add it to DNS, then kill the server and never tell IT about it. The majority of these are lab servers that are never joined to our AD domain, so I can't check DNS against computer accounts in AD.
How can I isolate and remove all of these stale static entries?
We're running Active Directory at a 2008r2 functional level. All of our DCs are 2008r2.