Moncy -
It is a manual operation to resync changes after recovery of the primary site, as is doing the 'snapmirror break' for failover.
These operations could be scripted.
There is some detail in the 'Data Protection Online Backup and Recovery Guide' portion of Data ONTAP documentation.
I hope this response has been helpful to you.
At your service,
Eugene E. Kashpureff
ekashp@kashpureff.org
NetApp Instructor and Independent Consultant
http://www.linkedin.com/in/eugenekashpureff
(P.S. I appreciate points for helpful or correct answers.)