within an integrated circuit 2 independently controllable domains 4 , 6 , 8 , 10 , 12 , 14 may be unable to complete pending transactions taking place between domains . each domain is provided with a transaction level state machine 20 , 22 which is responsive to the state of the state machine within the other domain and when this indicates that the other domain is not capable of communicating triggers default behavior ensuring that the predetermined transaction protocol is not broken .