The VFS Cache Tuning section in the EAP/EWP Admin and Config Guides ends with:
Another way to limit scanning is to provide the <filename>jboss-classloading.xml</filename> file, which contains classloader metadata.

There are currently no instructions about using this file to limit scanning.

http://community.jboss.org/wiki/JBoss5custommetadatafiles describes a simple jboss-classloading.xml file:
<classloading xmlns="urn:jboss:classloading:1.0" export-all="NON_EMPTY">
<capabilities>
<module name="test5"/>
</capabilities>
<requirements>
<module name="test2"/>
</requirements>
</classloading>

But I don't know whether this is specific to limiting scanning. See section 24.6.1.1.2. "Annotation Scanning Tuning" in http://documentation-stage.bne.redhat.com/docs/en-US/JBoss_Enterprise_Application_Platform/5.0/html-single/Administration_And_Configuration_Guide_CP01/#Memory_Usage_Tuning