1. A computer program product for facilitating processing of transactions within a computing environment, said computer program product comprising: a non-transitory computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: obtaining a transaction begin instruction, the transaction begin instruction comprising an opcode that specifies a transaction begin instruction of a particular type, and a field that specifies a general register save mask to explicitly specify a set of individually selected registers to be saved based on executing the transaction begin instruction, the transaction begin instruction to initiate a transaction, and the general register save mask explicitly specifying the set of individually selected registers to be saved at a start of the transaction; and executing the transaction begin instruction, the executing the transaction begin instruction comprising saving contents of the set of individually selected registers explicitly specified in the general register save mask of the transaction begin instruction, and initiating execution of the transaction.