Fix a bug in description of data races with scopes

The previously proposed wording suggested that any difference in scopes would
lead to undefined behavior, which was inconsistent with the paragraph
immediately afterwards about which atomics synchronize-with each other.

Author: Pennycook

adoc/chapters/architecture.adoc

@@ -1096,14 +1096,23 @@ programming and to provide a meaningful way to describe the behavior of
 <<group,groups>> containing a single work-item.
 {endnote}
 
-Potentially concurrent conflicting actions with different memory scopes are
-considered a data race, resulting in undefined behavior.
+Potentially concurrent conflicting actions with different memory scopes may
+lead to a data race, resulting in undefined behavior.
+An atomic operation _A_ with scope _S~1~_ operating on the same memory location
+as atomic operation _B_ with scope _S~2~_ is a data race if:
+
+* The work-items which executed _A_ and _B_ are not both in the same group of
+ work-items associated with scope _S~1~_; and
+* The work-items which executed _A_ and _B_ are not both in the same group of
+ work-items associated with scope _S~2~_.
 
 An atomic operation _A_ with scope _S~1~_ can only synchronize with another
 atomic operation _B_ with scope _S~2~_ if:
 
-* The work-item which executed _A_ is in both _S~1~_ and _S~2~_; and
-* The work-item which executed _B_ is in both _S~1~_ and _S~2~_.
+* The work-items which executed _A_ and _B_ are both in the same group of
+  work-items associated with scope _S~1~_; and
+* The work-items which executed _A_ and _B_ are both in the same group of
+  work-items associated with scope _S~2~_.
 
 The memory scopes are listed above from narrowest
 ([code]#memory_scope::work_item#) to widest ([code]#memory_scope::system#).