Methods and apparatuses are provided for flush operations in a processor. The apparatus comprises an out-of-order execution unit for processing instructions issued in-order from an instruction decoder for first and second threads and being configured to identify an errored instruction in a first thread. A retire unit includes a retire queue for receiving completed instructions from the out-of-order execution unit, the retire unit being configured retire older in-order first thread instructions until the errored instruction would be the next instruction to be retired, and then flushing the errored instruction and all later in-order first thread instructions from the retire queue. The method comprises determining that an errored instruction is being processed by an out-of-order execution unit of a processor and continuing to process to completion instructions earlier in-order from the errored instruction until the completion of the errored instruction. Following completion of the errored instruction, it is flushed along with all instructions later in-order than the errored instruction to recover the processor to a pre-error state.