It is useful to distinguish between specific gates, generic gates and callback gates:
DS domain, for example, has a specific gate (DSAT) that provides CHANGE_MODE and CHANGE_PRIORITY functions (among other functions). Only the DS domain provides those functions, but they can be requested by many different callers.
Most domains provide a QUIESCE_DOMAIN function, for example, so that they can be quiesced when CICS® is shutting down normally. They each have a generic gate that provides this function. DM domain makes a generic call to that gate in any domain that is to be quiesced.
For example the Recovery Manager calls the domains that have registered an interest in syncpoint processing using the PERFORM_PREPARE function format that it owns.