<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def force_invalidate(self, cache_key):
 """Force-invalidate the cached item."""

    try:
      if self.cacheable(cache_key):
        os.unlink(self._sha_file(cache_key))
    except OSError as e:
      if e.errno != errno.ENOENT:
        raise