$ mvn clean install
[INFO] Scanning for projects...
[ERROR] [ERROR] Some problems were encountered while processing the POMs:
[FATAL] Non-resolvable parent POM for org.alfresco:alfresco-repository:6.21-SNAPSHOT: Failure to find org.alfresco:alfresco-super-pom:pom:9 in https://repo.maven.apache.org/maven2 was cached in the local repository, resolution will not be reattempted until the update interval of central has elapsed or updates are forced and 'parent.relativePath' points at wrong local POM @ line 8, column 13