docs: def flush_cache(self, properties=None):
          """Flushes the cache being held for this instance.
  
          :param properties: The list of properties to flush from the cache.
          :type properties: list or None (default). If None, flush entire cache.
  
          """
          if hasattr(self, '_cache'):
              if properties is None:
                  del(self._cache)
              else:
                  for prop in properties:
                      if prop in self._cache:
                          del(self._cache[prop])