According to this report in Legal Times:

Goodling said that McNulty, during testimony before the Senate Judiciary Committee in February, “was not fully candid about his knowledge of White House involvement” in the decision to fire the U.S. Attorneys. She also said that McNulty was not forthright about his knowledge of the White House’s interest in the appointment of Timothy Griffin, a former aide to White House political adviser Karl Rove and Republican National Committee opposition researcher, to become U.S. Attorney in the Eastern District of Arkansas.
Additionally, she alleged, McNulty did not disclose the extent of his knowledge about allegations that Griffin had been involved in “caging” African-American votes during the 2004 elections, and inaccurately described the Justice Department’s assessment of a commission that reviewed candidates to become U.S. Attorney in California.

This appears to be the only reference to the “caging” allegation in the mainstream press and there’s no further discussion of the issue in the article. Greg Palast, writing at the Brad Blog, sees this as a very big deal. We’ll see if it gets picked up by the mainstream press.