When a replica of an application directory partition is added, the distinguished name of the nTDSDSA object for the domain controller that will contain the replica is added to the msDS-NC-Replica-Locations attribute of the crossRef object that represents the application directory partition.
To enumerate the replicas for an application directory partition, perform the following steps
Due to replication latency and scheduled KCC run delays, it is possible the actual active replicas for an application directory partition may not match the list of domain controllers indicated by the msDS-NC-Replica-Locations attribute of the crossRef object. A more accurate, but less efficient way to determine the actual active replicas of an application directory partition is to search for all nTDSDSA objects in the forest that have a msDS-hasMasterNCs attribute that contains the distinguished name of the application directory partition. The msDS-hasMasterNCs attribute contains the distinguished names of all writable directory partitions that the domain controller hosts, including application directory partitions.