Scope tree consistency protocol for cache coherence

One or more non-transitory computer readable media including instructions that, when executed, cause a scope tree controller to perform the steps of:

• receiving, at a first cache memory and from a second cache memory coupled to the first cache memory, a memory access request associated with a first scope group;
• and
• in response to determining that a first directory residing within the first cache memory includes a first entry indicating that (i) a third cache memory is a child of the first cache memory in a tree associated with the first scope group, and (ii) the first cache memory is a root of the tree associated with the first scope group:
• performing one or more operations to acquire a point of coherence token from a descendant cache memory of the first cache memory in the tree associated with the first scope group, and
• updating the first entry to indicate that the first cache memory is a point of coherence of the tree associated with the first scope group.

A system comprising:

• a portion of a scope tree controller that resides within a first cache memory in a cache hierarchy, wherein, in operation, the portion of the scope tree controller:
• receives, from a second cache memory coupled to the first cache memory, a memory access request associated with a first scope group;
• and
• in response to determining that a first directory residing within the first cache memory includes a first entry indicating that (i) a third cache memory is a child of the first cache memory in a tree associated with the first scope group, and (ii) the first cache memory is a root of the tree associated with the first scope group:
• performs one or more operations to acquire a point of coherence token from a descendant cache memory of the first cache memory in the tree associated with the first scope group, and
• updates the first entry to indicate that the first cache memory is a point of coherence of the tree associated with the first group.