Q. How can I un-register all the DNS records for a domain controller?

A domain controller's DNS records are stored in the netlogon.dns file, and in the registry.

If you wish to un-register all of a DC's DNS records, use NLTEST.EXE from the Support Tools with the /dsderegdns:<dns host name> switch, like:

nltest /dsderegdns:JSI007.JSIINC.COM

NOTE: See How can I cause a domain controller to re-register its DNS records without having to STOP and START its' NetLogon service?