RHEL 3.0AS | ext3-fs

I removed a 20G file when I noticed 100% usage in df. Usually it takes time before df will report the new (correct) usage, where du will report the new usage right away in dir where the offending file resided.

Code:
2.4G    app
94M     bin
4.0K    dict
4.0K    etc
4.0K    games
21M     include
95M     java
4.2M    kerberos
678M    lib
2.3M    libexec
37M     local
16K     lost+found
21M     sbin
646M    share
212M    src
0       tmp
70M     work
93M     X11R6

Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2             5.9G  236M  5.3G   5% /
/dev/sda1             122M   22M   94M  19% /boot
/dev/sda8             5.9G   72M  5.5G   2% /home
/dev/sda9             5.9G  215M  5.4G   4% /opt
none                  3.8G     0  3.8G   0% /dev/shm
/dev/sda7             5.9G   33M  5.5G   1% /tmp
/dev/sda5              26G   24G   54M 100% /usr
/dev/sda6             6.0G   69M  5.6G   2% /usr/local
/dev/sda10            8.2G  402M  7.4G   6% /var
cfms5:/fmis           184G   42G  133G  24% /fmis
"sync" command does not do what I expect, so does anyone know a way, without rebooting, unmounting fs etc to force df to re-read and report new usage? (it's own --sync does'nt work either)

I'm perfectly happy waiting, but I'd rather not have DBAs and developers calling me while it reports the wrong usage.