Ownership transference (either upgrade or downgrade) and borrowing are often unidirectional. In this discipline, we propose a bidirectional approach, that is, to release ownership, you must acquire another ownership in exchange. This exchange involves two parties (that is, owners), one propose the trade and the other can agree or refuse the trading. Note that who is making the request will accept any ownership in exchange, we are not concerned with any details of the exchange, and who is proposing the trade should know exactly what the other partner is offering in exchange. There are two kinds of ownership releasing, either permanent (that is transference) and temporary (in the case, borrowing). We can also sketch such temporary counterpart of trading, the parties can just trade again the previously exchanged ownership titles to "dismiss" the previous trade. Transference can be encoded with a fresh useless/empty object being exchanged, after that transaction, this useless object will be discarded and collected anyways.
Owners-as-traders can be really interesting in the context of distributed computing, MMORPGs and economic simulations. The mutually exclusive ownership concept catches very well the idea of resource allocation with a given net of players, surely it is useful in Game Theory. The implementation of such ownership policy can use two channels of communication, such channels will synchronize actors/threads until the exchange is performed or either cancelled.