Plagiarism Paranoia

I came up with one of those nice sounding sentences (the sort that don't bear great critical scrutiny) for the start of one of my assignments. Here it is:

If we are thinking about learning are we learning about thinking?

But then I wondered if it sound a little too familiar so I Googled it (how naughty using Google as an adjective) as a phrase with, and without, the question mark. Both times the phrase could not be found. I'm still a little paranoid but is the "not on Google" defence a reliable one for accidental plagiarists?