1. A method of securing a region in a memory of a computer comprising: causing all but one of a plurality of processing elements in a computer to enter into a special halted state as part of a join secure operation; receiving a region parameter that identifies a region in a memory of the computer for use in trust measurement; using a signed cryptographic hash of the identified region to verify whether content in the identified region can be trusted; placing the non-halted processing element into a known privileged state; and after the non-halted processing element has been placed into the known privileged state, generating a signal that causes the processing elements associated with the special halted state to exit the special halted state and resume activity, wherein each of the plurality of processing elements associated with the special halted state exits the special halted state as part of the join secure operation, in response to a signal from the non-halted processing element indicating that a start secure operation is complete, and wherein the join secure operation is performed atomically.