Ext JS Dependent combo box - extjs

Question

I am new to extJS, and trying to implement the following functionality:
I have two select drop down menus, transformed using extJS. How can I make sure that if a value in one combo box is selected, the other value should be set back to some default value?
Thanks.
Edited: Code till now:
Ext.onReady(function(){
var converted = new Ext.form.ComboBox({
typeAhead: true,
triggerAction: 'all',
transform:'id_Select1',
width:600,
forceSelection:true,
emptyText:'Select'
});
var convertedCdr = new Ext.form.ComboBox({
typeAhead: true,
triggerAction: 'all',
transform:'id_select2',
width:600,
forceSelection:true,
emptyText:'Select'
});
});
I am using ColdFusion to query the database and populate the drop down menus:
<cfquery name="getData1" datasource="abc">
SELECT * FROM table1
</cfquery>
<cfquery name="getData2" datasource="abc">
SELECT * FROM table2
</cfquery>
<select name="select1" id="select1">
<cfoutput query="getData1">
<option value="#getData1.Id#">#getData1.name#</option>
</cfoutput>
</select>
<select name="select2" id="select1">
<cfoutput query="getData2">
<option value="#getData2.Id#">#getData2.name#</option>
</cfoutput>
</select>

Answer 1

EDITED - I haven't used CFM... you'll need to figure out how to load your CF using data stores to use this technique.
You will need to add a listener for the select event on the combo:
xtype: 'combo',
id : 'firstComboID',
listeners: {
select: function(combo, record, index ) {
var selVal = Ext.getCmp('firstComboID').getValue();
var secondCombo = Ext.getCmp('secondComboID');
secondCombo.store.reload({params: {yourParameterName: selVal}});
}
Basically you are doing the following here:
Get the value selected in the first combo
Get a reference to the second combo's data store
Reload the store of the second combo box using the selected value from the first combo