<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _reset(cls):
 """If we have forked since the watch dictionaries were initialized, all that has is garbage, so clear it."""

        if os.getpid() != cls._cls_pid:
            cls._cls_pid = os.getpid()
            cls._cls_instances_by_target.clear()
            cls._cls_thread_by_target.clear()