SCSI3 persistent group reservations (PGR) may be removed only with host tools .. Or opening a SR and asking (at your own risk) to remove PGR from devices you want to "clean".

Can you please give better details on the environment ?? Host/OS/Cluster/Storage, just to name some.

Ref: emc92950

Can you please explain what you want to do in a different way ?? Do you want to disable the feature for some devices or do you want to clear the flag since your hosts are experiencing issues due to PER reservations left by other/olter clusters/nodes ??

AFAIK this primus explain how to ENABLE and DISABLE scsi3 PERsistent reservation for symmetrix devices.