When you sign onto a CICS region and type in a transaction name, CICS looks up the associated program for the transaction. It then looks to see if the program is in memory; if not, it loads the program from DFHRPL. So if a program is only used by one transaction and that transaction is not active, then the program memory usage in CICS is zero bytes. If you are not doing so, you can set up the STAT transaction to execute at CICS shutdown and review the program usage statistics for the region. If none of the programs in the application are listed as active, then none of the application programs are using CICS memory.
CICS doesn't really work in terms of applications -- it works with transactions, programs, TD queues, TS queues, files, and so forth. Even if there are no applications running in the CICS region, there is some memory used by system tables, CICS itself, system programs (such as the signon program or CEDA or CEDF), buffers for files that are opened when the region comes up, and so forth.