[RMcNeal]

In addition to the cold water line and valve under your sink, there's another valve next to the fridge. On my 3791RD, the valve was at the back of the lower cabinet on the left side of the fridge behind the rear panel. I had to remove the panel to find it. This valve turns on water to the actual small tubing to the fridge.
I believe the reasoning behind having 2 valves is that you can turn this one off when winterizing to prevent the pink stuff from getting into the ice maker. The low point drain line for the ice maker is between these two valves, this one and the one under your sink.