There are a couple of ways of doing it, but it would depend on what attributes you have in AD. Try something like this (not tested):
#REQUIRES QUEST AD Commandlets
# Collect the members of the good group
$good = Get-QADGroupMember -Identity ReceptionistGroup
# Collect the members of the bad group
$bad = Get-QADGroupMember -Identity SensitiveGroup
# Compare the good group to the bad and provide users that are members of both groups
# Then loop through and remove them from the other group
Compare-Object $good $bad -Property Name -ExcludeDifferent -IncludeEqual | foreach{ Remove-QADGroupMember -Identity SensitiveGroup -Member $_.Name}