You can probably get a toggle off/on going though a powershell script like so.
Open Windows Powershell ISE and copy paste the following code into it
{
#Disable the GPU
Get-PnpDevice -FriendlyName "The Name in Device Manager" | Disable-PnpDevice
#Adjust wait time to any amount you want
Sleep -Seconds 5
Get-PnpDevice -FriendlyName "The Name in Device Manager" | Enable-PnpDevice
}
Save the script to your desktop and right click > run with powershell
This should now toggle your GPU off/on. For other ways to clear the ram cache you'll have to check out the NVIDIA development forum. There are some things you can script with NVIDIA GPU's. A few sample scripts should be available for you to check out here on your local C Drive:
C:\Program Files\NVIDIA Corporation\NVIDIA WMI Provider\Samples