Circuitry for receiving transaction requests from a plurality of masters and the masters themselves are disclosed. The circuitry comprises: an input port for receiving said transaction requests, at least one of said transaction requests received comprising an indicator indicating if said transaction is a speculative transaction; an output port for outputting a response to said master said transaction request was received from; and transaction control circuitry; wherein said transaction control circuitry is responsive to a speculative transaction request to determine a state of at least a portion of a data processing apparatus said circuitry is operating within and in response to said state being a predetermined state said transaction control circuitry generates a transaction cancel indicator and outputs said transaction cancel indicator as said response, said transaction cancel indicator indicating to said master that said speculative transaction will not be performed.