Boyd Gaming has completed the sale of its half-ownership of Atlantic City's Borgata casino to MGM Resorts International.  Nevada-based Boyd says it received $589 million from Monday's transaction, after deducting its share of Borgata's currently outstanding debt. That amount does not include Boyd Gaming's 50 percent share of any future property tax settlement benefits.  The Borgata, Atlantic City's top casino, estimates it is due property tax refunds totaling $160 million.  MGM now owns all of the Borgata, which has dominated the Atlantic City market sine shortly after it opened in 2003.