Combine soy sauce, oyster sauce, sherry, cornstarch and sugar; marinate steak in mixture 30 minutes. Stir-fry broccoli cubes in 2 tablespoons oil over medium-high heat in wok or large skillet, 2-4 minutes. Add water and cook, covered, until crisp-tender. 1-2 minutes; remove from wok. In wok, heat remaining 2 tablespoons oil over high heat; stir in garlic and ginger. Add steak mixture; stir-fry, turning constantly, until lightly browned, 2-4 minutes. Return broccoli to wok; heat through.