dbmopen %FOO, "my_db", 0666 or die;
... populate %FOO
... delete some stuff from %FOO
{
  my %TEMP = %FOO; # cache it in memory
  dbmclose %FOO;
  unlink <my_db*>; # danger, but general enough {grin}
  dbmopen %FOO, "my_db", 0666 or die;
  %FOO = %TEMP;
}