WASHINGTON (MarketWatch) - Mainland China sold Treasurys in each of the last five months of 2011, according to a survey released by the Treasury Department on Wednesday. The data is based, in part, on a survey of U.S. custodians of the foreign holdings conducted last June. Treasury will start surveying custodians monthly in 2012 to get a more accurate picture of the holdings. In the past, the data has been collected from brokers and dealers. Treasury will still not have access to foreign custodial data. At the end of June 2011, foreigners held $7.73 trillion of Treasurys, up from $6.92 trillion of Treasurys in June 2010.