A centralised synchronizing device for determining progress of at least a subset of transaction requests that are transmitted through a data processing system. A system synchronizing request is a request generated by one of the plurality of transaction generating devices and queries progress of a subset of the transaction requests. The synchronizing device includes: at least one port to and from the data processing system; a multicast circuitry configured to output a plurality of synchronizing requests for multicast to at least some of the devices within the data processing system where the requests query the progress of the subset of the transaction requests. Gather circuitry collects responses to the requests confirming that the queried progress has occurred at the respective devices. The gather circuitry determines when responses to all of the requests have been received and outputs a response to the system synchronizing request.