Combine first 7 ingredients. Place steak in a large zip-top plastic bag, and pour half of marinade over meat. Seal, and chill 1 hour or up to 6 hours.
Pour remaining marinade into a small saucepan. Cook over medium-high heat 3 minutes or until reduced by one-third and slightly thickened. Cool, and stir in mint and cilantro.
Preheat grill to medium-high heat (350° to 400°). Remove meat from bag; discard marinade. Grill on greased grill grate 7 minutes on each side for medium-rare or until desired degree of doneness. Let stand 5 minutes before slicing. Drizzle with reduced marinade before serving.