Today i found how to specify default package for all Grails artefacts, would like to share with you.
By default when we create any domain, controller or any other artefact, It takes application name as default package. If you want to change that just define grails.project.groupId property in your Config.groovy.
grails.project.groupId = "your.package.name"
Looked into grails documentation but didn’t find it there, after some search found this jira issue. Seems this was some how missed in the documentation.