1. A method of controlling execution within a computing environment, the method comprising: detecting, by a processor, that execution of an instruction stream has aborted; based on detecting that execution of the instruction stream has aborted and prior to retrying execution of the instruction stream, initiating execution of a machine instruction to indicate to the processor that re-execution of the instruction stream is a retry, the machine instruction being defined for computer execution according to a computer architecture and comprising a field to specify a requested assist operation to be performed by the processor, a value of the field indicating that re-execution of the instruction stream is a retry and indicating an action is to be taken to facilitate successful re-execution of the instruction stream; based on initiating execution of the machine instruction, performing the action; and retrying execution of the instruction stream.