When the PDSE sharing protocol is in use, PDSE data is buffered after close of the data set. VARY OFFLINE causes the closed PDSE data in system buffers of the system on which the VARY occurs to be invalidated.
Before using program packages which change the VTOC and the data on the volume (for example, DFSMSdss full volume, and tracks RESTORE), it is recommended that the volume be VARIED OFFLINE to all other systems. Applications that perform these modifications to data residing on volumes without using the PDSE API should specify in their usage procedure that the volume being modified should be OFFLINE to all other systems, to help ensure there are no active connections to PDSEs residing on the volume while performing the operation.