PDC Emulator - dc=mycorp,dc=com
Infrastructure Master - cn=Infrastructure,dc=mycorp,dc=com
RID Master - cn=RID Manager$,cn=System,dc=mycorp,dc=com
Schema Master - cn=Schema,cn=Configuration,dc=mycorp,dc=com
Domain Naming Master - cn=Partitions,cn=Configuration,dc=mycorp,dc=com
The information in the attribute is stored as a DN, representing the NTDS Settings object of the domain controller that is the role owner. So, example contents for this attribute might be:
CN=NTDS Settings, CN=MYSERVER1, CN=Servers, CN=My Site,
CN=Sites, CN=Configuration, DC=mycorp, DC=com