Thanks grandep, I was going to post the same thing.
I would like to point out something else. Domestic and international trends change over time. Domestic might outperform for awhile, then international, etc. Sometimes that outperformance can last 6-7 years in a row. Think of it this way. When everyone is convinced one thing will do better because it has been doing better, maybe they put more in it driving the price up. BTW, the OP's question is an example of this behavior. That leaves the out of favor asset class priced lower giving it more room to run, which leads to a period of out performance in the future.
On that note, while US has outperformed international most of the past 7 years you will pay a lot more for US corporate earnings than international right now. VFIAX(500 index) PE ratio = 21. VTIAX(International) PE ratio = 14.
Let's look at a historical example of international outperformance. On that chart look specifically at 2002-2007. In each of those years the emerging markets and the MSCI ex-US world index both outperformed the S&P 500. This was after a period where the US outperformed most years(the late 90s). It is entirely possible that could happen again, and given the valuation differences I wouldn't be surprised if we were going into a period of international outperformance.