http://www.numonyx.com/en-US/ResourceCenter/Software
Articles/Pages/ReduceNANDdefects.aspx
Refresh block on 1-bit error corrects errors due to Read Disturb

The Block Refresh on 1-bit errors feature takes into account
the fact that many transient errors occur due to Read Disturb
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(due to NAND architecture, all cells in the same word line are
affected when reading a particular cell) or, in some cases,
voltage degradation over time.

The concept is that if a block reaches a point where transient
errors begin to occur, erasing the block (setting all bits to
"1") and rewriting it may solve the problem. Specifically,
Block Refresh rewrites the block data in a different block that
is not experiencing errors, and then erases (reclaim) the
erroneous block for usage in a later operation.