それからHyperTransport自体もコヒーレントなバスでわ無いす。
http://www.commsdesign.com/news/OEG20020721S0007
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  The group [HyperTransport Consortium] has so far decided not to
  define a coherent version of the link and to instead let members,
  such as AMD, go their own way on that front.
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AMDが上位のレイヤーに実装しているだけということす。