1. A computer program product for executing a machine instruction, 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, a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising: at least one opcode field for specifying an opcode, the opcode defining a branch operation; and at least one field for determining a target location in which to branch; and executing the machine instruction in a first stream of processing, the executing comprising: starting a second stream of processing, the second stream of processing having a relationship with the first stream of processing; and starting a transaction for the second stream of processing, the transaction to include execution of one or more instructions beginning at the target location defined using the at least one field of the machine instruction, the one or more instructions being out of sequential execution order from one or more instructions being processed by the first stream of processing, the first stream of processing continuing to process one or more instructions subsequent to the machine instruction; and wherein execution of the second stream of processing is speculative in that at least one instruction of the one or more instructions of the second stream of processing is executed even though reaching the at least one instruction of the second stream of processing by processing of the first stream is tentative, and wherein updating of architected state by one or more instructions of the second stream of processing is performed based on the first stream of processing reaching a predefined point in processing.