[I]t appears from the earliest quotations ... that the brow in question was that of the beater, not of the beaten party; but it is not evident whether the meaning was 'to beat with one's (frowning) brows,' or 'to beat (?lower) one's brows at.' [OED]
Related: Browbeaten; browbeating.[browbeat etymology, browbeat origin, 英语词源]