Disable or flush page cache on Windows

This is called Standby List under windows. You can purge it globally, or for one volume, or for one file handle.

Globally
You can do it using a readily available program from Microsoft Technet, by selecting Empty → Empty Standby List

Programmatically, you can achieve the same thing using the undocumented NtSetSystemInformation function, for details see line 239 in a program which does the same thing as the previously mentioned one, among other things.

For one file handle
Open the file with FILE_FLAG_NO_BUFFERING: The documentation is lying insofar as it says that you open the file without buffering, but the true, observable behavior on all Windows versions from Windows 98 up to Windows 8 is that it simply throws away the complete cache contents for that file (for everyone!) and doesn't repopulate the cache from reads that use this handle.

For one complete volume
A volume handle is just a file handle (a somewhat special one, but still), so assuming you have appropriate privilegues to open a volume handle, you can do the same for a complete volume.

Also, as pointed out in the answer here, there seems to be a feature/bug (feature-bug?) which allows you to invalidate a volume's cache even without proper privilegues merely by attepting to open it without shared writes, at least under one recent version of Windows.
It makes perfect sense that this happens when any open which is valid for writing succeeds as you may change filesystem-internal data doing so (insofar it is a feature), but apparently it also works when opening the volume fails (which is a bug).