How to force discarding of invalid cached partition contents?

A USB hard drive contains a FAT32 partition. Sometimes the partition has a drive letter assigned. When the partition has a drive letter, Windows Explorer and/or some other parts of Windows XP read and cache a portion of the contents. I write part of the partition myself, so I want to force Windows to abandon its cached contents.

I call DeviceIoControl several times. FSCTL_LOCK_VOLUME, FSCTL_DISMOUNT_VOLUME, IOCTL_VOLUME_OFFLINE, IOCTL_VOLUME_ONLINE, and FSCTL_UNLOCK_VOLUME. All of these succeed. WinIoCtl.h doesn't define IOCTL_VOLUME_OFFLINE and IOCTL_VOLUME_ONLINE, but MSDN implies that these are supposed to be available to user mode applications, so I define them myself and DeviceIoControl reports success.

After that, I have found two ways to do manual operations to force Windows to abandon its cached contents. One is to use Computer Administrator - Disk Administrator, remove the drive letter from the partition, and reassign the drive letter to the partition. The other way is to open a command prompt and run CHKDSK /F, which finds no errors but which somehow persuades Windows XP to discard its cache. If I omit the /F then the obsolete contents remain in the cache, after which Windows proceeds to corrupt the partition and then the next CHKDSK /F adjusts errors (but lost data remain lost).

Now I want to do this programmatically. I wonder why obsolete contents remain in the cache after IOCTL_VOLUME_OFFLINE and IOCTL_VOLUME_ONLINE, but continue trying anyway. I added calls to BroadcastSystemMessage with DBT_DEVICEREMOVECOMPLETE and DBT_DEVICEARRIVAL. These report success. Furthermore if Windows Explorer was displaying the partition before these operations, I can see Windows Explorer respond by removing that partition from its display, displaying the contents of another partition, and then restoring the drive letter and icon in the left hand pane though the right hand pane continues displaying the other partition that it had switched to. So I think that DBT_DEVICEREMOVECOMPLETE and DBT_DEVICEARRIVAL have some amount of effect. But when I click on that drive letter in Windows Explorer, it still displays obsolete cached information, and creating a new file causes corruption in the partition.

What does it take to force Windows to discard obsolete cached data?

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