Decommissioning the Source Domain
Applies To: Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2
Applies to: Active Directory Migration Tool 3.2 (ADMT 3.2)
After you complete the migration of the accounts and resources in your source domain, decommission the source domain. Ensure that you retain a full system state backup of a domain controller so that you can bring the domain back online at any time.
To decommission the source domain
Remove all trust relationships between the source domain and the target domain.
Repurpose any remaining domain controllers in the source domain that you did not migrate to the target domain.
Disable all accounts that you created during the migration process, including those accounts to which you assigned administrative permissions.
When you decommission the source domain, shared local groups and local groups that you have not translated by using the Security Translation Wizard display group members as "account unknown." This is because member names from the source domain do not resolve. Those group memberships still exist, however, and this does not affect users. Do not delete "account unknown" entries because this disables the access that is facilitated by security identifier (SID) history. Run the Security Translation Wizard to remove these entries.