An initiator device for issuing transaction requests to a recipient device via an interconnect is disclosed. The initiator device comprises: at least one port for receiving requests from and issuing requests to said interconnect; a barrier generator for generating barrier transaction requests, the barrier transaction requests indicating to the interconnect that an ordering of at least some transaction requests within a stream of transaction requests passing through the interconnect should be maintained by not allowing reordering of at least some of the transaction requests that occur before the barrier transaction request in the stream of transaction requests with respect to the barrier transaction request; wherein in response to receipt of a synchronise request querying progress of at least a subset of transaction requests, the initiator device is responsive to action any pending transaction requests within the at least a subset of transaction request and to generate a barrier transaction request at the barrier generator and to issue the barrier transaction request to the interconnect via the at least one port, and in response to receiving a response to the barrier transaction request to issue an acknowledge signal as a response to the synchronise request.