Apparatus methods for capturing flow control errors in FIFO exchanges between producing and consuming circuits operating in different clock domains. Tag information at the start of an exchange is transferred to a synchronizing component before data of a transfer transaction is entered in the FIFO. The tag information is also associated with each unit of data transferred to the FIFO by the producing circuit. The synchronizing component verifies the each unit of data retrieved by the consuming circuit has the expected tag information associated therewith and signals an error is the tag information does not match. Thus an error by the producing circuit in entering too much or too little data for a transfer is detected before erroneous data is retrieved and processed by the consuming circuit.