When to Intervene?

An expatriate friend recently shared that she had witnessed a domestic abuse case next door. It was evening, she was washing the dishes, and suddenly horrible screaming started. She could hear several women and kids yelling out of fear and she could also hear sounds like a whip lashing. Since it's a building site next door, where this was taking place, she could actually see two women huddled together. Unsurprisingly, my friend said the experience was highly disturbing. What do you do? When do you intervene? What's the best action to take, especially in a country that's not your own?

Their response was that her husband went out to find out into the street to see what was happening, and to ask other neighbors what should be done. There was already a small crowd gathered outside the building site gate and several people tried to peer in through slots in the gate. But, they said there was nothing more they could do. Except be curious with degrees of worry, peer in, wait. Apparently there was no reason to call the police since they wouldn't do anything anyway. And apparently it was 'the old way of domestic life,' i.e. wife and/or child beatings have been very common since it was the man's way of, literally, putting his foot down. And apparently these were 'poor country folk' who didn't know better. Hm. What would you have done in this situation? How would you have acted if it happened next door to you, in the West? How about in a foreign country?

This reminds me of our house hunting when we were moving to the Cambodian countryside ourselves. We'd found a potential house but before making enquiries we were quietly warned that there's a (domestically) abusive man in the next house over. They would have been the only neighbors on that street. We were told it 'might not be nice' to live next to that family 'but it could quiet down the beating.' So, would our presence have stopped the abuse since it would have been so shameful for this family to have their low points witnessed by a bunch of foreigners? I don't know. It could have literally quieted down the abuse, i.e. it would have continued but not that loudly. How do you stop abuse from the outside anyway? And what would you do if spine-chilling sounds like these started regularly - I for one would under no circumstances want my boys to hear that. What would it do to them? So, pick up your own bags and move? Or hope for the best and 'shame' abusers out silently?