Rinse chicken and pat dry; season with salt and pepper. Heat 1 tablespoon oil in a heavy 5-quart pot over moderately high heat until hot but not smoking. Add chicken, in 2 batches, and cook, turning, until golden brown on all sides, about 8 minutes per batch. Transfer, as cooked, with tongs to a plate, leaving fat in pot. Add onion, garlic and cumin to pot; cook over moderate heat, stirring, until onion is softened, about 2 minutes. Add wine and simmer until reduced by one-third, about 5 minutes. Stir in broth, juice, capers and tomatoes. Return chicken to pot and simmer, covered, until cooked through, 30 to 35 minutes. Stir in cilantro and butter; serve over rice.