Not sure what you mean by clean. RAM is the memory used when you start your computer up and is volatile memory.
https://techterms.com/definition/ram The information below comes from this link.
Below are images from my computer using Task Manager to show the Memory (RAM) in use. The first image shows what is cached while being used and the second is what is in use after a shutdown and reboot.
1st image.
2nd image after shutdown and reboot.
I hope this has helped.