Either MVS™ cross-memory services or the CICS® Type 3 SVC can be used for interregion communication (function shipping, transaction routing, distributed transaction processing, and asynchronous processing).
If you use cross-memory services, you lose the total separation between systems that is normally provided by separate address spaces.
The risk of accidental interference between two CICS address spaces connected by a cross-memory link is small. However, an application program in either system could access the other system's storage (subject to key-controlled protection) by using a sequence of cross-memory instructions.
If this situation would create a security exposure in your installation, use the CICS type 3 SVC for interregion communication, rather than MVS cross-memory services.
For information about how to specify the access method for MRO, see the the CICS Intercommunication Guide.