What version of ColdFusion are you using? When I run my code in ColdFusion 9, I get the header value (as seen using FireBug ):
test: 1, 2
As for whether you can tell what, if any, existing values for the response header, I have not yet found a way. However, I will continue to search.
: .
getPageContext().getResponse().containsHeader("test")
:
<cfif getPageContext().getResponse().containsHeader("test") eq "NO">
<cfheader name="test" value="2" />
</cfif>