[AccessD] Parent form PK changed (VALUE)

Is there a way (built into Access) to tell if the parent form record changed
from the subform?  IOW, in the case of a M-M table, implemented in a
subform, one of the fields of the M-M would be the parent ID.

tblCompany
CO_ID
CO_Name
CO_Etc

tblPeople
PE_ID
PE_Lname
PE_Fname
PE_Etc

tblEmployees
EM_ID
EM_IDPE
EM_IDCO

If the parent form is the company, the child form is the employee, the
"link" is the EM_IDCO with a combo representing the people.  I want to
monitor when the parent ID changes (CO_ID) from the subform sfrmEmployee.  I
know that the subform control has a Link Child Field / Link Master Field
pair of properties, but is there a property that feeds the VALUE of the Link
Master Field into the subform for it's use?  The subform filters its
recordset based on the Link Master Field VALUE so it must be able to see it.

In fact all I want to know is THAT the Link Master Field VALUE changed so
that I can requery a dependent combo in the child form.

John W. Colby
www.ColbyConsulting.com