A data processing system can establish or maintain data coherency by issuing a data flush operation. An agent can initialize a first flush operation by writing to a flush register. The agent can determine that the flush operation is complete by reading a status indicator from a status register. Additional agents can independently issue flush operations during the pendency of the first flush operation. A second flush instruction and any additional flush instructions that issue during the pendency of the first flush operation set a flush pending indicator in a status register. Once the first flush operation completes, the host performs all pending flush operations in a single second flush operation. The status indicator does not indicate a completed flush operation for the first flush operation until all flush operations are complete. Multiple co-pending flush operations are collapsed into at most two flush operations.