Can I test whether a control has been changed outside the relevant event?

I have a series of drop down lists on a form: let's call them ddlOne, ddlTwo, ddlThree, and ddlFour.  If ddlOne is set, then I want ddlTwo, ddlThree, and ddlFour to be set to the same value UNLESS they are set explicitly.  Similarly, ddlTwo's value should be set for ddlThree and ddlFour,  and ddlThree's value should be set for ddlFour.
I could easily achieve this result if I could use the event name as a condition, writing something like this: -
Protected Sub ddlOne_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles
              ddlOne.SelectedIndexChanged
    If Not ddlTwo.SelectedIndexChanged Then ddlTwo.SelectedIndex = ddlOne.SelectedIndex
    If Not ddlThree.SelectedIndexChanged Then ddlThree.SelectedIndex = ddlOne.SelectedIndex
    If Not ddlFour.SelectedIndexChanged Then ddlFour.Selec ...