Globally unique transaction identifiers

In one embodiment of the present invention, a method includes identifying a transaction from a first processor to a second processor of a system with a transaction identifier. The transaction identifier may have a value that is less than or equal to a maximum number of outstanding transactions between the two processors. In such manner, a transaction field for the transaction identifier may be limited to n bits, where the maximum number of outstanding transactions is less than or equal to 2n. In various embodiments, such a transaction identifier combined with a source identifier and a home node identifier may form a globally unique transaction identifier.