1. A method comprising: a first processor operating in an advanced synchronization mode, which includes specifying and acquiring exclusive access to a given memory resource, wherein specifying comprises executing a code sequence including: one or more locked memory reference instructions having a LOCK prefix and one or more addresses associated with the given memory resource, and an ACQUIRE instruction that is subsequent to the one or more locked memory reference instructions; a second processor requesting access to the given memory resource and issuing a probe message; and in response to receiving the probe message, the first processor responding to the probe message with a failure message denying the second processor access to the given memory resource.