Grease a 2-quart baking dish. Toss together the bread cubes, crabmeat, Swiss cheese, Cheddar cheese, capers, and green onions in the baking dish.
Mix together eggs, milk, sherry, mustard, and Worcestershire sauce in a bowl. Pour evenly over bread mixture. Cover tightly and refrigerate at least 2 hours, but no longer than 24 hours.
Preheat oven to 350 degrees F (175 degrees C). Bake strata uncovered until knife inserted in the center comes out clean, about 45 minutes. Let stand 10 minutes before serving. Serve while still hot.
