diff -r 29f1c6149efb -r cda786f0fb05 src/mem/cache/cache_impl.hh
--- a/src/mem/cache/cache_impl.hh	Tue Mar 26 14:13:42 2013 -0400
+++ b/src/mem/cache/cache_impl.hh	Tue Mar 26 14:13:42 2013 -0400
@@ -1310,6 +1310,9 @@
         if (is_timing) {
             Packet snoopPkt(pkt, true);  // clear flags
             snoopPkt.setExpressSnoop();
+            if (pkt->isSnoopNoResp())
+                snoopPkt.setSnoopNoResp();
+
             snoopPkt.pushSenderState(new ForwardResponseRecord(pkt->getSrc()));
             // the snoop packet does not need to wait any additional
             // time
@@ -1335,7 +1338,10 @@
         }
     }
 
-    if (!blk || !blk->isValid()) {
+    // If the packet is a snoop that doesn't want a response (because it's a
+    // prefetch that will get dropped), just return here. See comment in
+    // prefetch code for race that can occur if we don't.
+    if (!blk || !blk->isValid() || pkt->isSnoopNoResp()) {
         return;
     }
 
@@ -1628,11 +1634,16 @@
             // in place of the dirty one.
             PacketPtr snoop_pkt = new Packet(tgt_pkt, true);
             snoop_pkt->setExpressSnoop();
+            snoop_pkt->setSnoopNoResp();
             snoop_pkt->senderState = mshr;
             cpuSidePort->sendTimingSnoopReq(snoop_pkt);
 
             if (snoop_pkt->memInhibitAsserted()) {
-                markInService(mshr, snoop_pkt);
+                // Someone else has the line, we should forget about our
+                // prefetch. Otherwise, there is a race between this cache
+                // getting the line and another request coming in and hitting
+                // in the mshr that isn't known to be dirty yet
+                mshr->queue->deallocate(mshr);
                 DPRINTF(Cache, "Upward snoop of prefetch for addr %#x hit\n",
                         tgt_pkt->getAddr());
                 delete snoop_pkt;
diff -r 29f1c6149efb -r cda786f0fb05 src/mem/packet.hh
--- a/src/mem/packet.hh	Tue Mar 26 14:13:42 2013 -0400
+++ b/src/mem/packet.hh	Tue Mar 26 14:13:42 2013 -0400
@@ -245,6 +245,7 @@
     static const FlagsType SUPPLY_EXCLUSIVE       = 0x00000004;
     // Snoop response flags
     static const FlagsType MEM_INHIBIT            = 0x00000008;
+    static const FlagsType SNOOP_NO_RESP          = 0x00000010;
     /// Are the 'addr' and 'size' fields valid?
     static const FlagsType VALID_ADDR             = 0x00000100;
     static const FlagsType VALID_SIZE             = 0x00000200;
@@ -514,6 +515,8 @@
     // Special control flags
     void setExpressSnoop()      { flags.set(EXPRESS_SNOOP); }
     bool isExpressSnoop()       { return flags.isSet(EXPRESS_SNOOP); }
+    void setSnoopNoResp()       { flags.set(SNOOP_NO_RESP); }
+    bool isSnoopNoResp()        { return flags.isSet(SNOOP_NO_RESP); }
     void setSupplyExclusive()   { flags.set(SUPPLY_EXCLUSIVE); }
     void clearSupplyExclusive() { flags.clear(SUPPLY_EXCLUSIVE); }
     bool isSupplyExclusive()    { return flags.isSet(SUPPLY_EXCLUSIVE); }