The White Sox traded Dominguez, Nolan Jones and Boston Smith to the Mariners on Saturday in exchange for Luis Castillo, Jeff Passan of ESPN.com reports.
Dominguez opened the season as the Mariners' closer but lost his grip on the job in late June, shifting to a high-leverage role out of the bullpen. He'll now head to Seattle, where he'll presumably operate in that leverage role with the Mariners with Andres Munoz serving as the top closer. Dominguez has a 4.10 ERA, 1.37 WHIP, 12 saves (in 17 chances), four holds and a 45:23 K:BB over 37.1 innings this season.