1. A computer program product for performing processing associated with transactional execution in a computing environment, the computer program product comprising: a computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: obtaining, by a processor, an instruction to be executed as part of a transaction; computing one or more effective controls from one or more controls set by one or more transaction begin instructions, wherein the one or more effective controls comprises an effective allow access register modification control that indicates whether an access register is permitted to be modified; determining by the processor whether the instruction is a selectively restricted instruction that is prohibited from execution within the transaction, the determining being based on the computed one or more effective controls; and performing processing associated with the instruction based on whether the instruction is selectively restricted.