Subprime loans dominate loss mitigation activity at thrifts, according to a servicing survey by the Office of Thrift Supervision.The federal regulator surveyed Countrywide Financial, IndyMac, Merrill Lynch, Wachovia and Washington Mutual. The servicers handled 11.4 million first lien residential mortgages, with total outstanding balances of $2.3 trillion at... [Includes one chart]