Chrome frozen by popup ad

Chrome is currently frozen on my Galaxy s5 by a popup ad offering a prize, If I click "OK". I want to know how I can unfreeze the screen. All the advice I can find explains how to clear the cache in Chrome, but I can't access Chrome. I have tried "Force Stop" in the application manager. It there another back entry that I can use? I want to know how to fix this immediate problem, not how to prevent it from happening again.

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