AppDomain.Unload Does Not Free Up The Used Memory

I'm kinda new here, and I didn't know what forum to put this in, so I just put it here. I wanted to load an assembly to an Application Domain, use it, then unload it when I'm done with it. The assembly uses too much memory. The problem is: After I unloaded the assembly, the memory used is not getting freed. I was watching the performance all the time. The available memory increases only after I close the whole application. And that assembly is the only thing that uses a lot of memory in my application. Here's the code I used to load and unload the assembly: How can I free up the memory without closing my application. The memory was suppose to get freed up by simply unloading the assembly that uses it much.