On Alpha and Integrity server systems, removes a specified range
    of pages from the current working set of the calling process to
    make room for pages required by a new program segment.

    This service accepts 64-bit addresses.

    Format

      SYS$PURGE_WS  start_va_64 ,length_64

    C Prototype

      int sys$purge_ws  (void *start_va_64, unsigned __int64

                        length_64);