setKeyframe at a time, and force re-evaluation?

[RFlannery1]

I use "setKeyframe" to set the "translateX" value at a given time.  Immediately afterwards, I query the "translateX" value and "matrix" value at that time.  The "translateX" returns the correct value, but the "matrix" does not.

Here is my sample code:

def setValueAtTime(value, time):
    node = 'pCube1'
    cmds.setKeyframe(node, attribute='translateX', time=time, value=value)
    xValAfter = cmds.getAttr(node+'.translateX', time=time)
    matAfter = cmds.getAttr(node+'.matrix', time=time)
    print 'new translateX: {0}\t\t new matrix[12]: {1}'.format(xValAfter, matAfter[12])

for i in range(3):
    setValueAtTime(i, 5)

Assuming the cube starts out with an x-translation of 2.0, it prints out the following result:

new translateX: 0.0		 new matrix[12]: 2.0
new translateX: 1.0		 new matrix[12]: 2.0
new translateX: 2.0		 new matrix[12]: 2.0

The documentation for "setKeyframe" says, "Using the value flag will not cause the keyed attribute to change to the specified value until the scene re-evaluates. Therefore, if you want the attribute to update to the new value immediately, use the setAttr command in addition to setting the key."  But "setAttr" doesn't have a time parameter, and I don't want to set the value at the current time.  Also, I don't want to re-evaluate the entire scene because it is large and complicated.

Questions:

1. What is the best way to force the "matrix" attribute to update, without re-evaluating the entire scene?  (I have a couple of hacky workarounds but am hoping there's a better way.)
2. Why does "translateX" update to the correct value but "matrix" does not?