how to clear 'future' dates in QHST log? (due to y2k testing)

Someone set the system date of one of our machine to 31Dec1999 to test
out Y2K programs but upon resetting the date back to the present, the
system history log is now cluttered with those 1999 log entries. And
because the dsplog is sorted in date order, it is bit confusing to look
at.
Any idea on how we can clear these up from the system history log? 
(The QHST object is a message queue but can't seem to use the normal
message queue commands on it.)
Thanks.
KKLiu
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