Me › Storage & Cache clears the image cache: pictures downloaded by widgets and widget preview images. They're downloaded or recreated automatically when needed.
To clear only the data one tool has recorded, touch and hold it on the Tools page and choose Clear data. This can't be undone.
To remove a tool completely, touch and hold it on the Tools page and choose Delete. Its widgets are removed along with it. With Sync across devices on, deleting a tool removes it from all your devices, along with the data it recorded.