As far as I am concerned it's rather simple, whenever a real selloff is expected it would be evident via futures pre-open as stock holders will be hedging against a selloff, what we have seen on Friday as a reaction to China is not worrying. Let's see what happens tonight. US indexes have made it above 200 Daily SMA, DAX has made it above it last week, FTSE is below it and China too.
August sell off was marked by China eventually falling through that SMA, the world followed as the rest were drifting near it.