A processing unit for a data processing system includes a cache memory having reservation logic and a processor core coupled to the cache memory. The processor includes an execution unit that executes instructions in a plurality of concurrent hardware threads of execution including at least first and second hardware threads. The instructions include, within the first hardware thread, a first load-reserve instruction that identifies a target address for which a reservation is requested. The processor core additionally includes a load unit that records the target address of the first load-reserve instruction and that, responsive to detecting, in the second hardware thread, a second load-reserve instruction identifying the target address recorded by the load unit, blocks the second load-reserve instruction from establishing a reservation for the target address in the reservation logic.