Create a file called "jboss-deployment-structure.xml" in the META-INF directory for an EAR or WEB-INF directory for a WAR. This file can contain a lot of different stuff to tweak the classloader, but for the logback case this is enough:
<?xml version="1.0" encoding="UTF-8"?>
<jboss-deployment-structure>
<deployment>
<exclusions>
<module name="org.apache.commons.logging" />
<module name="org.apache.log4j" />
<module name="org.jboss.logging" />
<module name="org.jboss.logging.jul-to-slf4j-stub" />
<module name="org.jboss.logmanager" />
<module name="org.jboss.logmanager.log4j" />
<module name="org.slf4j" />
<module name="org.slf4j.impl" />
</exclusions>
</deployment>
</jboss-deployment-structure>
For the EAR case, you'll probably need to add a subdeployment for each application (both wars and ejbs) with the same exclusions. For more details, consult the JBoss documentation on the subject.