A processing unit for a multiprocessor data processing system includes a processor core including a store-through upper level cache, an instruction sequencing unit that fetches instructions for execution, a data register, and at least one instruction execution unit coupled to the instruction sequencing unit that concurrently executes multiple threads of instructions. The processor core, responsive to the at least one instruction execution unit executing a load-reserve instruction in a first thread that binds to a load target address in the store-through upper level cache during a reservation hazard window associated with a conflicting store-conditional operation of a second thread, causes a subsequent store-conditional operation of the first thread to a store target address matching the load target address to fail if the store-conditional operation of the second thread succeeds.