Immutable functions and cache invalidation.

Say I have a function like this.

CREATE OR REPLACE FUNCTION some_constant(
)
RETURNS text
LANGUAGE 'plpgsql'
COST 100
IMMUTABLE
ROWS 0
AS $BODY$
begin
return 'some_string';
end;
$BODY$;

Then I have another function that calls it but is also immutable

CREATE OR REPLACE FUNCTION some_proc(
)
RETURNS text
LANGUAGE 'plpgsql'
COST 100
IMMUTABLE
ROWS 0
AS $BODY$
declare
x textl;
begin

x := some_constant();
....
end;
$BODY$;

will postgres know to invalidate the cache on some_proc() if I change the
returned value in some_constant()?

Thanks.