The embodiment enables multiple virtual data domains to be accessible to a program executing on a processor. A data domain is a set of virtual address spaces for containing data that can be accessed by an executing program. Two types of data domains are defined by access lists, called PSAL and DUAL. Each list has entries specifying virtual address spaces accessible to an executing program. The program is located in a program address space. The program address space and each data domain are located through respective control registers. On a program call, the processor loads a control register with means to identify the PSAL data domain. The loaded control register provides the called program with immediate access to its own PSAL data domain. When the call is from a different program address space, the calling program space's PSAL data domain immediately becomes non-accessible due to overlaying in the single loading of the one control register. Switching of the PSAL data domains is fast and easy because only one address is loaded into the control register. Because the DUAL data domain remains unchanged across the program call, the calling and called programs have common access to the DUAL data domain.