Since it's already been answered, I'm just gonna make an example where that particular meaning of そんな could be used.
A: The truth is that I'm not your real father...
B: そんな。。。
And you could imagine the shocked child falling to his/her knees.
That そんな can be translated as: "It cannot be..." or "Impossible..." or "No way...". As I see it, it's close to what Nothing at all commented.
