Dockery spent the 2010 season with St. Louis after playing his first four years with the New York Giants. He has four interceptions, one returned for a touchdown, in 61 career games.
Harris has appeared in 18 games, including nine starts, over two NFL seasons. He played just three games last year for Washington after spending the 2009 campaign with Philadelphia.
Pittsburgh also waived/injured wide receiver Limas Sweed and waived tight end Eugene Bright. Sweed, Pittsburgh's second-round pick in the 2008 draft, missed the entire 2010 season because of an Achilles injury and played just 20 games for the Steelers.