Try disabling the panGestureRecognizer
for the scroll view (and then reenabling it). This will cancel the current session of the recogniser:
ObjC
self.scrollView.panGestureRecognizer.enabled = NO;
self.scrollView.panGestureRecognizer.enabled = YES;
Swift
self.scrollView.panGestureRecognizer.isEnabled = false
self.scrollView.panGestureRecognizer.isEnabled = true