Reset value of an Ember object

I have an Ember object "Xmodel" which contains a property 'selectedValue' It contains the value as "ABC,XYZ"

I want to set this to an empty string ('')

But I am unable to do that. I have already tried

Xmodel.selectedValue = '';
Ember.set('Xmodel', 'selectedValue', '');

Plus tried few variations with Ember.set()

Just to add actually 'Xmodel' is one of the instances from an array that iterate using for..each