I'm trying to passthrough my nv video card to my domU, but I could not bind my video card to the pciback driver

I only have one video card with the pci number 0000:03:00.0, so I used the following command

echo -n "0000:03:00.0" > /sys/bus/pci/drivers/nouveau/bind

to unbind the nouveau driver from my video card.

The screen went black because I have forcefully removed the video driver, therefore I ssh'd into the computer to run further commands

I ran:

echo -n "0000:03:00.0" > /sys/bus/pci/drivers/pciback/bind

to try to bind it to my pciback driver, but I got:

bash: echo: write error: No such device

I found out that this was the message shown when trying to bind a PCI device which is already bound. Therefore, I think that something was still using my video card

Can anyone help me out? Thanks a lot!