A system may include at least a first agent and a second agent, and the first agent may be coupled to receive a block signal generated by the second agent. The block signal is indicative of whether or not the second agent is capable of participating in transactions. The first agent initiates or inhibits initiation of a transaction for which the second agent is a participant responsive to the block signal. The system may include additional agents, each configured to generate independent block signals. Other implementations may share block signals among two or more agents. For example, a memory block signal indicative of memory transactions being blocked or not blocked and an input/output (I/O) block signal indicative of I/O transactions being blocked or not blocked may be employed. In yet another implementation, a first agent may provide separate block signals to other agents.