The foreign-exchange trading business was in upheaval across Wall Street as senior executives resigned and others were fired amid an expanding probe of possible currency manipulation. Benjamin Lawsky, superintendent of New York’s Department of Financial Services, asked more than a dozen firms including Deutsche Bank AG (DB), Goldman Sachs Group Inc. (GS) and Citigroup Inc. (C) for documents on their currency-trading practices, said a person with knowledge of the matter. Deutsche Bank, the top foreign-exchange trader, fired four dealers after an internal probe, people with knowledge of the move said. Goldman Sachs ... (full story)