Remove all classes except one
Instead of doing it in 2 steps, you could just reset the entire value at once with attr by overwriting all of the class values with the class you want:
jQuery('#container div.cleanstate').attr('class', 'cleanstate');Sample: http://jsfiddle.net/jtmKK/1/
Use attr to directly set the class attribute to the specific value you want:
$('#container div.cleanstate').attr('class','cleanstate');
With plain old JavaScript, not JQuery:
document.getElementById("container").className = "cleanstate";