1. A method for scaling address space utilization in a multi-threaded, multi-processor computer, the method comprising: attaching, to process memory of an exporting process, a region of virtual memory specified in a cross-memory descriptor; requesting, by an importing thread of an importing process having process memory, attachment of the region of virtual memory for exclusive use by the importing thread; and attaching, by an operating system to the process memory of the importing process, the region of virtual memory for exclusive use by the importing thread, thereby creating a lightweight attachment of the region of virtual memory.