According to Shulchan Aruch O.C. 143:4 (Mechaber), if someone finds a mistake in the Torah during the aliyah he is reading, he should stop, take out another Torah, finish the aliyah, and have the oleh say the ending bracha.
Does this same procedure apply if the reader discovers an error outside the current aliyah being read, e.g. before or after the current aliyah?