You need to purge the list of user accounts that were authenticated on a read-only domain controller (RODC).
What should you do?

A.
Run the repadmin.exe command and specify the /prpparameter.

B.
From Active Directory Sites and Services, modify the properties of the RODC computer object.

C.
From Active Directory Users and Computers, modifythe properties of the RODC computer object.

D.
Run the dsrm.exe command and specify the -u parameter.

Explanation:
Reference:
http://technet.microsoft.com/en-us/library/rodc-guidance-for-administering-the-password-replication-policy.aspx
Clearing the authenticated accounts list
In addition to reviewing the list of authenticated users, you may decide to periodically clean up the list of
accounts that are authenticated to the RODC. Cleaning up this list may help you more easily determine the new
accounts that have authenticated through the RODC.
Membership in the Domain Admins group of the domainin which the RODC is a member, or equivalent, is the
minimum required to complete this procedure.
To clear all entries from the list, run the commandrepadmin /prp delete <hostname> auth2 /all.
Substitute the actual host name of the RODC that you want to clear. For example, if you want to clear the list of
authenticated accounts for RODC2, type repadmin /prp delete rodc2 auth2 /all, and then press
ENTER.