That's odd. Google should normally default to google.(your local tld) for the country you're in.
In my niche, even without clicking on 'results from my country', the serps are pretty much already from my country.
When I click on 'results only from my country', pretty much all that happens is they get rid of wikipedia.
So, it's not Google screwing up - they know what they're doing. There's something about those other sites that tells Google they're relevant to visitors from your country.
I've no idea what that is, other than my mantra 'more, stronger links'.