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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _reset_docs(self):
 """ Helper to clear the docs on RESET or filter mismatch. """

        _LOGGER.debug("resetting documents")
        self.change_map.clear()
        self.resume_token = None

        # Mark each document as deleted. If documents are not deleted
        # they will be sent again by the server.
        for snapshot in self.doc_tree.keys():
            name = snapshot.reference._document_path
            self.change_map[name] = ChangeType.REMOVED

        self.current = False